Method of preventing high Icc at start-up in zero-power EEPROM cells for PLD applications
View Patent ↗A CMOS memory cell (FIG. 1 ) is provided which includes a PMOS transistor ( 102 ) and an NMOS transistor ( 104 ) with a common floating gate and common drains configured to prevent a large drain of Icc current from a power supply during power-up. To prevent the large Icc during power-up, the threshold voltages of the PMOS transistor ( 102 ) and NMOS transistor ( 104 ) are set so that the PMOS transistor ( 102 ) and NMOS transistor ( 104 ) do not turn on together, irrespective of charge initially stored on the floating gate. Without such thresholds, a significant drain of current Icc from the power supply connection Vcc can occur since charge initially on the floating gate leaves both the PMOS transistor ( 102 ) and the NMOS transistor ( 104 ) on creating a path for Icc from Vcc to Vss.
1. An array of CMOS memory cells, each memory cell in the array comprising:
a PMOS transistor having a source coupled to Vcc, a drain and a floating gate, the PMOS transistor having ion implantation in a substrate between its source and drain to set a first threshold value for the PMQS transistor;
an NMOS transistor with a source coupled to Vss, a drain in common with the PMOS transistor and a floating gate in common with the PMOS transistor;
a control capacitor having one terminal in common with the floating gate;
a tunneling capacitor having one terminal in common with the floating gate and a second terminal; and
a pass transistor having a source-drain path connected to the second terminal of the tunneling capacitor,
wherein the first threshold value is set so that charge cannot be provided to the floating gate causing both the NMOS and the PMOS transistor to be turned on together.
2. The array of claim 1 , wherein the NMOS transistor has ion implantation in a substrate between its source and drain to set a second threshold value for the NMOS transistor.
3. The array of claim 2 ,
wherein the first threshold voltage is altered by implanting ions in a channel between the source and drain of the NMOS transistor, and
wherein the second threshold value is altered by Implanting ions between the source and drain of the PMOS transistor.
4. The array of claim 3 ,
wherein the ions implanted in the channel of the NMOS transistor are arsenic; and
wherein the ions implanted in the channel of the PMOS transistor are boron.
5. The array of claim 2 wherein the first threshold value and the second threshold value are set so that charge cannot be provided on the floating gate causing both the PMOS transistor and the NMOS transistor to turn on together when Vcc is provided within a specified operation range.
6. The array of claim 2 wherein the first threshold value and the second threshold value are set so that charge cannot be provided on the floating gate causing both the PMOS transistor and the NMOS transistor to turn on together when Vcc is ramped up from zero volts to a value within a specified operation range.